Strain-induced catalytic enhancement in Co-BTA and Rh-BTA for efficient 2e- oxygen reduction: a DFT study.

Here we design TM-BTA catalysts for the electrochemical synthesis of hydrogen peroxide (H2O2), focusing on the efficient two-electron (2e-) oxygen reduction pathway. Employing density functional theory (DFT), we screened 17 transition metals, identifying Co-BTA and Rh-BTA as outstanding candidates based on their low overpotentials and superior catalytic activity. A key innovation is the application of mechanical strain to these catalysts, significantly optimizing their performance by modulating the d-band center. This approach enhances the adsorption of oxygen-containing intermediates, crucial for the 2e- ORR process. Our findings demonstrate that a tensile strain of 1.95% optimally enhances catalytic efficiency in both Co-BTA and Rh-BTA, substantially reducing overpotential. This research not only highlights the potential of TM-BTA catalysts in H2O2 production but also underscores the importance of strain modulation as a cost-effective and efficient method to improve the selectivity and activity of electrocatalysts, offering a novel perspective in the field of sustainable chemical synthesis.

Effect of alloying on the dynamics of coherent acoustic phonons in bismuth double perovskite single crystals.

The bismuth double perovskite Cs2AgBiBr6 has been regarded as a potential candidate for lead-free perovskite photovoltaics. A detailed study on the coherent acoustic phonon dynamics in the pure, Sb- and Tl-alloyed Cs2AgBiBr6 single crystals is performed to understand the effects of alloying on the phonon dynamics and band edge characteristics. The coherent acoustic phonon frequencies are found to be independent of the alloying, while the damping rates are highly dependent on the alloying. Based on the mechanism of coherent acoustic phonon damping, a technique has been successfully developed that can accurately extract the absorption spectra near the indirect band gap for these single crystals with coefficients on the order of 102 cm-1.

Reconstructing Reliable Powder Patterns from Spikelets (Q)CPMG NMR Spectra: Simplification of UWNMR Crystallography Analysis.

Spikelets NMR spectra are very popular as they enable the shortening of experimental time and give the possibility to obtain required NMR parameters for nuclei with ultrawide NMR patterns. Unfortunately, these resulted ssNMR spectra cannot be fitted directly in common software. For this reason, we developed UWNMRSpectralShape (USS) software which transforms spikelets NMR patterns into single continuous lines. Subsequently, these reconstructed spectral envelopes of the (Q)CPMG spikelets patterns can be loaded into common NMR software and automatically fitted, independently of experimental settings. This allows the quadrupole and chemical shift parameters to be accurately determined. Moreover, it makes fitting of spikelets NMR spectra exact, fast and straightforward.

Lead-Free Halide Double Perovskite Cs2 AgBiBr6 with Decreased Band Gap.

Environmentally friendly halide double perovskites with improved stability are regarded as a promising alternative to lead halide perovskites. The benchmark double perovskite, Cs2 AgBiBr6 , shows attractive optical and electronic features, making it promising for high-efficiency optoelectronic devices. However, the large band gap limits its further applications, especially for photovoltaics. Herein, we develop a novel crystal-engineering strategy to significantly decrease the band gap by approximately 0.26 eV, reaching the smallest reported band gap of 1.72 eV for Cs2 AgBiBr6 under ambient conditions. The band-gap narrowing is confirmed by both absorption and photoluminescence measurements. Our first-principles calculations indicate that enhanced Ag-Bi disorder has a large impact on the band structure and decreases the band gap, providing a possible explanation of the observed band-gap narrowing effect. This work provides new insights for achieving lead-free double perovskites with suitable band gaps for optoelectronic applications.

Understanding Antiferromagnetic Coupling in Lead-Free Halide Double Perovskite Semiconductors.

Solution-processable semiconductors with antiferromagnetic (AFM) order are attractive for future spintronics and information storage technology. Halide perovskites containing magnetic ions have emerged as multifunctional materials, demonstrating a cross-link between structural, optical, electrical, and magnetic properties. However, stable optoelectronic halide perovskites that are antiferromagnetic remain sparse, and the critical design rules to optimize magnetic coupling still must be developed. Here, we combine the complementary magnetometry and electron-spin-resonance experiments, together with first-principles calculations to study the antiferromagnetic coupling in stable Cs2(Ag:Na)FeCl6 bulk semiconductor alloys grown by the hydrothermal method. We show the importance of nonmagnetic monovalence ions at the BI site (Na/Ag) in facilitating the superexchange interaction via orbital hybridization, offering the tunability of the Curie-Weiss parameters between -27 and -210 K, with a potential to promote magnetic frustration via alloying the nonmagnetic BI site (Ag:Na ratio). Combining our experimental evidence with first-principles calculations, we draw a cohesive picture of the material design for B-site-ordered antiferromagnetic halide double perovskites.

Bis(1-ethyl-4,4'-bipyridin-1-ium) bis-(1,2-di-cyano-ethene-1,2-di-thiol-ato-κ(2) S,S')nickelate(II).

In the anion of the title compound, (C12H13N2)[Ni(C4N2S2)2], the Ni(II) atom is coordinated by four S atoms from two 1,2-di-cyano-ethene-1,2-di-thiol-ate (mnt) ligands in a suqare-planar geometry. Weak C-H⋯N and C-H⋯S hydrogen bonds between the 1-ethyl-4,4'-bipyridin-1-ium cations and mnt anions and weak π-π inter-actions between the pyridine rings of the cations [centroid-centroid distances = 3.808 (3) and 3.972 (3) Å] lead to a two-dimensional network parallel to (010).

Strong self-trapping by deformation potential limits photovoltaic performance in bismuth double perovskite.

Bismuth-based double perovskite Cs2AgBiBr6 is regarded as a potential candidate for low-toxicity, high-stability perovskite solar cells. However, its performance is far from satisfactory. Albeit being an indirect bandgap semiconductor, we observe bright emission with large bimolecular recombination coefficient (reaching 4.5 ± 0.1 × 10-11 cm3 s-1) and low charge carrier mobility (around 0.05 cm2 s-1 V-1). Besides intermediate Fröhlich couplings present in both Pb-based perovskites and Cs2AgBiBr6, we uncover evidence of strong deformation potential by acoustic phonons in the latter through transient reflection, time-resolved terahertz measurements, and density functional theory calculations. The Fröhlich and deformation potentials synergistically lead to ultrafast self-trapping of free carriers forming polarons highly localized on a few units of the lattice within a few picoseconds, which also breaks down the electronic band picture, leading to efficient radiative recombination. The strong self-trapping in Cs2AgBiBr6 could impose intrinsic limitations for its application in photovoltaics.

The atomic-level structure of bandgap engineered double perovskite alloys Cs2AgIn1-x Fe x Cl6.

Although lead-free halide double perovskites are considered as promising alternatives to lead halide perovskites for optoelectronic applications, state-of-the-art double perovskites are limited by their large bandgap. The doping/alloying strategy, key to bandgap engineering in traditional semiconductors, has also been employed to tune the bandgap of halide double perovskites. However, this strategy has yet to generate new double perovskites with suitable bandgaps for practical applications, partially due to the lack of fundamental understanding of how the doping/alloying affects the atomic-level structure. Here, we take the benchmark double perovskite Cs2AgInCl6 as an example to reveal the atomic-level structure of double perovskite alloys (DPAs) Cs2AgIn1-x Fe x Cl6 (x = 0-1) by employing solid-state nuclear magnetic resonance (ssNMR). The presence of paramagnetic alloying ions (e.g. Fe3+ in this case) in double perovskites makes it possible to investigate the nuclear relaxation times, providing a straightforward approach to understand the distribution of paramagnetic alloying ions. Our results indicate that paramagnetic Fe3+ replaces diamagnetic In3+ in the Cs2AgInCl6 lattice with the formation of [FeCl6]3-·[AgCl6]5- domains, which show different sizes and distribution modes in different alloying ratios. This work provides new insights into the atomic-level structure of bandgap engineered DPAs, which is of critical significance in developing efficient optoelectronic/spintronic devices.

Magnetizing lead-free halide double perovskites.

Spintronics holds great potential for next-generation high-speed and low-power consumption information technology. Recently, lead halide perovskites (LHPs), which have gained great success in optoelectronics, also show interesting magnetic properties. However, the spin-related properties in LHPs originate from the spin-orbit coupling of Pb, limiting further development of these materials in spintronics. Here, we demonstrate a new generation of halide perovskites, by alloying magnetic elements into optoelectronic double perovskites, which provide rich chemical and structural diversities to host different magnetic elements. In our iron-alloyed double perovskite, Cs2Ag(Bi:Fe)Br6, Fe3+ replaces Bi3+ and forms FeBr6 clusters that homogenously distribute throughout the double perovskite crystals. We observe a strong temperature-dependent magnetic response at temperatures below 30 K, which is tentatively attributed to a weak ferromagnetic or antiferromagnetic response from localized regions. We anticipate that this work will stimulate future efforts in exploring this simple yet efficient approach to develop new spintronic materials based on lead-free double perovskites.

Structural and Functional Diversity in Lead-Free Halide Perovskite Materials.

Lead halide perovskites have emerged as promising semiconducting materials for different applications owing to their superior optoelectronic properties. Although the community holds different views toward the toxic lead in these high-performance perovskites, it is certainly preferred to replace lead with nontoxic, or at least less-toxic, elements while maintaining the superior properties. Here, the design rules for lead-free perovskite materials with structural dimensions from 3D to 0D are presented. Recent progress in lead-free halide perovskites is reviewed, and the relationships between the structures and fundamental properties are summarized, including optical, electric, and magnetic-related properties. 3D perovskites, especially A2 B+ B3+ X6 -type double perovskites, demonstrate very promising optoelectronic prospects, while low-dimensional perovskites show rich structural diversity, resulting in abundant properties for optical, electric, magnetic, and multifunctional applications. Furthermore, based on these structure-property relationships, strategies for multifunctional perovskite design are proposed. The challenges and future directions of lead-free perovskite applications are also highlighted, with emphasis on materials development and device fabrication. The research on lead-free halide perovskites at Linköping University has benefited from inspirational discussions with Prof. Olle Inganäs.

High performance electrochemical biosensor based on 3D nitrogen-doped reduced graphene oxide electrode and tetrahedral DNA nanostructure.

In this study, an electrochemical biosensor was developed for highly sensitive and specific detection of target miRNA-155. The structure was formed by the hybridization of a tetrahedral DNA nanostructure-based biomolecular probe assembled on 3D nitrogen-doped reduced graphene oxide/ gold nanoparticles (3D N-doped rGO/AuNPs) electrode surface. Upon addition of target miRNA-155, the gold and silver nanorod/ thionine/ complementary DNA (AuAgNR/Thi/F) was hybridized with the target, and used for signal amplification, catalyzing the reduction of Thi as an electron mediator. Due to the signal amplification by the enhanced immobilization of DNA on the surface of 3D N-doped rGO/AuNPs electrode and AuAgNR/Thi, coupling the low background signal produced by blank solution, electrochemical performance of the device was optimized to be proportional to miRNA-155 concentration in the range of 1 × 10-11 to 1 × 10-4 M with a detection limit of 1 × 10-12 M. In addition, direct detection in serum is demonstrated with high specificity. Thus, this biosensor is potentially applicable for microRNA detection in medical research and early clinical diagnosis.

Long Electron-Hole Diffusion Length in High-Quality Lead-Free Double Perovskite Films.

Developing environmentally friendly perovskites has become important in solving the toxicity issue of lead-based perovskite solar cells. Here, the first double perovskite (Cs2 AgBiBr6 ) solar cells using the planar structure are demonstrated. The prepared Cs2 AgBiBr6 films are composed of high-crystal-quality grains with diameters equal to the film thickness, thus minimizing the grain boundary length and the carrier recombination. These high-quality double perovskite films show long electron-hole diffusion lengths greater than 100 nm, enabling the fabrication of planar structure double perovskite solar cells. The resulting solar cells based on planar TiO2 exhibit an average power conversion efficiency over 1%. This work represents an important step forward toward the realization of environmentally friendly solar cells and also has important implications for the applications of double perovskites in other optoelectronic devices.

Robust Crystalline Hybrid Solid with Multiple Channels Showing High Anhydrous Proton Conductivity and a Wide Performance Temperature Range.

A proton conductor displaying high anhydrous proton conductivity (≈10(-2) S cm(-1)) and good performance over a broad temperature range is presented. This hybrid material is produced via doping HCl into open-framework chalcogenide(C2N2H10)(C2N2H9)2 Cu8 Sn3S12, and has cubopolyhedral cavities and multiple channels.

Observation of hysteretic magnetic phase transitions coupled with orientation motion of ions and dielectric relaxation in a one-dimensional nickel-bis-dithiolene molecule solid.

The second polymorph, the ß-crystal, of the nickel-bis-dithiolene compound [4'-CF3bzPy][Ni(mnt)2], where 4'-CF3bzPy = 1-(4'-trifluoromethylbenzyl)pyridinium and mnt(2-) = maleonitriledithiolate, was obtained. The variable-temperature single crystal structures, magnetic behavior in 1.8-300 K and dielectric nature in 123-373 K have been investigated for the ß-crystal. This polymorph experiences two hysteretic magnetic phase transitions in a narrow temperature region (190-217 K) with the thermal hysteresis loops ca. 6 K and ca. 11 K. The two hysteretic magnetic phase transitions are coupled with two isostructural phase transitions (IPTs), respectively, which are driven by the novel step-wise dynamic orientation motion of the anion and cation in the ß-crystal. There is an absence of a dielectric anomaly in the structural transformation temperature interval. However, a dielectric relaxation, related to the dipole motion of polar CF3 groups in the cations under an ac electrical field, emerges in the high-temperature phase.

Two segregated columnar stack platinum-bis-dithiolene molecule solids showing spin-Peierls-type transition above room temperature.

Two new one-dimensional (1-D) compounds, [CH3-BzPy][Pt(mnt)2] (1) and [CH3-BzPy-d5][Pt(mnt)2] (2) (CH3-BzPy(+) = 1-N-(4-CH3-benzyl)pyridinium and the pyridine in CH3-BzPy(+) was replaced by pyridine-d5 to give the CH3-BzPy-d5(+); mnt(2-) = maleonitriledithiolate), were synthesized and characterized. 1 and 2 show similar magnetic behavior in 1.8-400 K; they experience a spin-Peierls-type transition around 320 K and show a uniform antiferromagnetic S = 1/2 chain behavior in high temperature (HT) phase, a spin gap feature in low temperature (LT) phase. A symmetry breaking structural phase transition is associated with the spin-Peierls-type transition. Two isostructural compounds crystallize in space group P2(1)/c in HT phase, with a = 12.3066(8) Å, b = 27.0522(18) Å, c = 7.4248(4) Å, ß = 104.204(6)° and V = 2396.3(3) Å(3) for 1 versus a = 12.3331(9) Å, b = 27.087(4) Å, c = 7.4501(9) Å, ß = 104.149(13)° and V = 2413.3(6) Å(3) for 2 at 353 K, while space group P1[combining macron] in LT phase, with a = 7.3203(10) Å, b = 12.2816(16) Å, c = 26.904(4) Å, α = 88.500(4)°, ß = 86.731(4)°, γ = 75.421(4)° and V = 2337.0(5) Å(3) for 1 versus a = 7.3308(8) Å, b = 12.2848(13) Å, c = 26.930(3) Å, α = 88.479(3)°, ß = 86.652(4)°, γ = 75.563(3)° and V = 2344.5(4) Å(3) for 2 at 296 K. DSC measurements revealed 1 and 2 showing almost the same T(C). This observation is distinction from the [Ni(mnt)2](-)-based spin-Peierls-type analogues [CH3-BzPy][Ni(mnt)2] and [CH3-BzPy-d5][Ni(mnt)2] where the deuteration leads to T(C) up shifting 2.3 K.

Comparative study of structures, thermal stabilities and dielectric properties for a ferroelectric MOF [Sr(µ-BDC)(DMF)]∞ with its solvent-free framework.

A ferroelectric MOF with a formula [Sr(µ-BDC)(DMF)]∞ (1) was transformed into [Sr(µ-BDC)(CH2Cl2)x]∞ (2) using a solvent exchange approach, where DMF = N,N-dimethylformamide and BDC(2-) = benzene-1,4-dicarboxylate. The lattice solvents, CH2Cl2 molecules, in 2 were removed by heating to give the solvent-free metal-organic framework [Sr(µ-BDC)]∞ (3) and the crystal-to-crystal transformation is reversible between 1 and 3. The release of DMF molecules from 1 results in the metal-organic framework of [Sr(µ-BDC)]∞ expanding a little along the a- and b-axes. The crystal structure optimizations for 1 and 3 disclosed that the lattice expansion is associated with the alternations of the bond distances and angles in the Sr(2+) ion coordination sphere along the a- and b-axes directions. The metal-organic framework 3 collapses at temperatures of more than 600 °C; such an extremely high thermal stability is related to the closed-shell electronic structure of the Sr(2+) ion, namely, the coordinate bond between the closed-shell Sr(2+) ion and the bridged BDC(2-) ligands does not have a preferred direction, which is favored for reducing lattice strains and is responsible for the higher thermal stability. The comparative investigations for the dielectric and ferroelectric behaviors of 1 and 3 confirmed that the motion of the polar DMF molecules, but not the [Sr(µ-BDC)]∞ framework, is responsible for the ferroelectric properties of 1.